Seal for electric discharge devices and method of manufacture



March30, 1948. E, KETTL WELL 2,438,562

SEAL FOR ELECTRIC DISCHARGE DEVICES AND METHOD OF MANUFACTURE FiledMarch 27, 1944 hven'ta': I Eric ke't'tlewell, by M' v HisAfiorneg.

Patented Mar. 30, 1948 SEAL FOR ELECTRIC DISCHARGE DEVICES AND METHOD OFMANUFACTURE Eric Kettleweil, Kingsbury, London, England, aslignor toGeneral Electric Company, a corporation of New York Application March27, 1944, Serial No. 528,182

In Great Britain March 13, 1942 Section 1, Public Law 690, August 8,1946 Patent expires March 13, 1962 12' Claims. 1

This invention relates to electric discharge devices, and moreespecially to seals and terminal structures for such devices and totheir manufacture. It is especially useful for devices employing quartzenvelopes, such as high pressure metal vapor lamps referred tohereinafter as HPMV lamps.

A limit is set on the power that can be dissipated in a HPMV lamp by theoverheating of the electrodes, especially the anode ii the device isoperated on D. C. The limit could be iii-=- creased if the electrodecould be placed in close thermal connection with the exterior of theenvelope, as is the anti-cathode in many X-ray.

tubes; for then water-or forced air-cooling could be applied to it. But,while the envelopes of X-ray tubes are usually of glass, having acomparatively high coeiliclent of thermal expansion, those of the l-IPMVlamps in which the limitation is serious are generally of quartz. Manyof the devices used in li -ray tubes for the purpose are not readilyapplicable to .EJPMV lamps of quartz. The object of this invention is tomodify these devices so that they are applicable to lamps with quartzenvelopes.

The drawing is an elevation, in section, of a seal and electrodestructure made in accordance with this invention.

The method depends on the fact that a layer of tungsten, and possiblycertain other metals, can be deposited on quartz so that (l) a metalthat wets the layer (e. an, as copper wets tune sten) can be made toform a gas=tiaht junction with the quartz and (2) the layer can besealed into quartz by the technique employed in making a strip seal.

According to one aspect of the invention, the manufacture oi a devicecomprising a sealed envelope of quartz comprises the following steps:(1) coating with an adherent layer of refractory metal, for exampletungsten, the whole of the circumference of a quartz tube or of a partthereof; (2) collapsing onto the said tube part of another quartz tube,so that part of the said layer is embedded in (quartz, and another partlies in the space between the two tubes; (3) filling the said space witha molten metal (for example copper) which wets the said metal layer, andcausing the said molten metal to cover the open end of the first saidtube that lies within the second said tube (4) partially embedding in,or otherwise placing in intimate thermal contact with, the said moltenmetal a refractory metal. for example, a tungsten body; and (5) sealingthe second said tube into the aperture of a quartz Q envelope. Steps (3)and (4) may be performed in the same operation.

According to another aspect of the invention, a device, comprising aquartz envelope, comprises Within the envelope a body of refractorymetal (A) in close thermal contact with metal which is continuous withmetal (E) which (a) closes the inner end of a tube passing through thesaid envelope and unclosed at its outer end, (b) fills the space betweenthe said tube (inner tube) and an outer tube surrounding it, the saidtubes being fused together outside the said space and (c) wets a metallayer deposited on the outer side of the said inner tube and therebymakes a gas-tight junction with the inner tube.

One embodiment of the invention will now be described by way oi examplewith reference to the accompanying drawing. 6 is the said inner tube, 2the said outer tube. The outer tube carries on its outer surface themembers 3 by means of which it is joined to the remainder of theenvelope, a portion of which is indicated by the dotted lines ill. Theinner tube is coated along part of its length with the layer :3 oftungsten or equivalent metal; part of the outer tube has been collapsedonto the inner tube, so that at E the tubes are completely united and atthe layer l is embedded between them. i is a tune;- sten block which mayserve as an electrode and from which a lead 3 passes to the exterior ofthe device down the inner tube 5. 9 is copper or equivalent metalfilling: space between the inner and outer tubes and wetting the layer lwhere it is in contact with it; the block ii is partially embedded init.

In making the device, the layer is formed on the tube l and the tube 2collapsed onto it. The upper open end of the tube i is blocked by astopper (indicated at it) through which the lead 8 passes, supportingthe block just above the open end. Molten copper is then poured into theouter tube so as to fill up the space that it occupies in the figure.Air could enter the envelope only by passing between the copper and thequartz; it is prevented from doing so by intimate contact oi the copperwith the tungsten layer t and of this layer with the quartz on which itis deposited.

It will be obvious those skilled in the art that other refractory metalsmay be used for the coating 4, such for example, as molybdenum orplatinum. Moreover, other metals than copper may be usec. for thefilling; metal such for example, as silver. The metals copper andsilver, 01 course, have lower melting points than tun aesasee sten,molybdenum or platinum and, unlike mercury for example, are solid atordinary temperatures.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. The method of making a seal for high intensity electric dischargedevices which comprises coating the outer surface of an inner quartztube which is open at both ends with an adherent layer of refractorymetal, collapsing onto the said tube part of an outer quartz tube sothat part of the said layer is embedded in quartz and another part isexposed in the space between the two tubes, and filling the said spacewith a molten metal which has a substantially lower melting point thansaid refractory metal and which wets the said refractory metal and issolid at ordinary temperatures, and causing the said molten metal tocover over the adjacent open end of the inner tube, whereby tohermetically seal the said adjacent end of the inner tube by anair-tight bond between the said molten metal, the refractory metal andthe wall of the said inner tube.

2. The method of making a seal for high intensity electric dischargedevices which comprises coating the outer surface of an inner quartztube which is open at both ends with an adherent layer of refractorymetal, collapsing onto the said tube part ofan outer quartz tube so thatpart of the said layer is embedded in quartz and another part is exposedin the space between the two tubes, and filling the said space with amolten metal which has a substantiallyv lower melting point thansaidrefractory metal and which wets the said refractory metal and is solidat ordinary temperatures, and causing the said molten metal to coverover the adjacent open end of the inner tube and partially embedding arefractory metal electrode body in the said molten metal, whereby tohermetically seal the said adjacent end of the inner tube by anair-tight bond between the said molten metal, the refractory metal andthe wall of the said inner tube.

3. A seal and electrode structure for high intensity electric dischargedevices comprising an inner quartz tube open at both ends and having onits outer surface a circumferentially extending adherent layer ofrefractory metal, an outer quartz tube surrounding said inner tube,portions of said tubes being fused together with at least a portion ofthe layer of refractory metal in the space between portions of the tubesnot fused together, a quantity of a second metal which is solid atordinary temperatures and which wets to the said refractory metalsolidified in situ in the space between the tubes and covering over theadjacent end of theinner tube, the said second metal being wetted to therefractory metal layer on the inner tube and thereby forming a gas-tightjunction with the tube, and a refractory metal electrode in closethermal contact with the said second metal.

4. A seal and electrode structure for high intensity electric dischargedevices comprising an inner quartz tube open at both ends and having onits outer surface a circumferentially extending adherent layer ofrefractory metal, an outer quartz tube surrounding said inner tube,portions of said tubes being fused together with a part of the saidlayer of metal embedded in the joint and another part in the spacebetween portions of the tubes not fused together, a quantity of a secondmetal which is solid at ordinary temperatures and which wets to the saidrefractory metal solidified in situ in the space between the tubes 4 andcovering over the'adjacent end of the inner tube, the said second metalbeing wetted to the refractorymetal layer on the inner tube and therebyforming a gas-tight junction with the tube, and a refractory metalelectrode in close thermal contact with the said second metal.

5. A seal and electrode structure for high intensity electric dischargedevices comprising anv inner quartz tube open at both ends and having onits outer surface a circumferentially extending adherent layer oftungsten, an outer quartz tube surrounding said inner tube, portions ofsaid tubes being fused together with at least a portion of the layer oftungsten in the space'between portions of the tubes not fused together,a quantity i of copper solidified in situ in the space between the tubesand covering over the adjacent end of the inner tube, the said copperbeing wetted to the tungsten layer on the inner tube and thereby forminga gas-tight junction with the tube, and a refractory metal electrode inclose thermal contact with the said copper.

6. The method of making a seal for high intensity electric dischargedevices which comprises bringing into telescoping relation a surroundingouter quartz tube and an inner quartz tube externally coated over anintermediate portion of its length within the outer tube with acircumferentially extending adherent layer of refractory metal, therelative sizes of said tubes for at least part of their lengthsaffording space between them around one end of the inner tube and atleast part of its said adherent refractory metal layer; fusing togetherportions of said tubes, while leaving the aforesaid space between them;filling v said space with other metal, in molten condition,

which has a substantially lower melting point than said refractory metaland which wets to the said refractory metal and is solid at ordinarytemperatures, and also causing this molten metal to cover over theadjacent end of the inner tube; and bringing a refractory metalelectrode into close thermal contact with the said other metal, which isallowed to solidify in situ, whereby to hermetically seal the saidadjacent end of the inner tube by an air-tight bond between the saidmolten metal, the refractory metal and the wall of the said inner tube.

7. A seal for high intensity electric discharge devices comprising aninner quartz tube open at both ends and having its outer surface coatedwith an adherent layer of refractory metal, a larger outer quartz tubearound said inner tube having part thereof collapsed onto the inner tubeso that part of said layer is embedded in quartz, while another partextends into a space between the two tubes, and a quantity of anothermetal which has a lower melting point than the said refractory metal andwhich wets the said refractory metal and is solid at ordinarytemperatures filling the said space, and covering over the adjacent endof the said inner tube, thereby hermetically sealing the said end of theinner tube by an air-tight bond between. the second mentioned metal, therefractory metal and the wall of said inner tube.

8. A composite assembly comprising a quartz tube, a circumferentiallyextending deposit of refractorymetal in intimate contact with the outersurface of said tube adjacent one open end thereof, and a body ofanother metal which wets the said refractory metal and is solid atordinary temperatures enclosing and covering over the said end of thetube and forming a gas-tight junction with said tube directly throughsaid deposit of 10. A composite assembly comprising a quartz tube, abody of copper enclosing and covering over one open end of said tube,and an intervening deposit of tungsten in direct intimate gas-tightcontact between the outer surface of said tube and the adjoining surfaceof said body hermetically sealing said body to said tube, the said bodyof copper being wetted to the said deposit of tungsten.

11. A composite assembly for an electric discharge device comprising aquartz tube, a body of metal enclosing and covering over one open end ofsaid tube, and an intervening deposit of refractory metal in directintimate gas-tight contact between the outer surface of said tube andthe adjoining surface of said body hermetically sealing said body tosaid tube, said body being of metal which wets the said refractory metaland is solid at ordinary temperatures, and an electrade of refractorymetal partially embedded in said body.

12. The method of making a seal for high intensity electric dischargedevices which comprises depositing a layer of refractory metal inintimate gas-tight contact with the outer surface of a quartz tube andadjacent one open end thereof, and casting around and over the said endof the tube, including a portion having the layer of refractory metalthereon, a molten metal which wets the said refractory metal and issolid at ordinary temperatures, whereby to form a body of the cast metalenclosing the said end of the tube and making a gas-tight junctiontherewith.

ERIC KE'I'ILEWELL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,159,335 Keyes Nov. 2, 19151,740,397 Fehse Dec, 17, 1929 1,803,541 Aba May 5,1931 2,023,931McCullough Dec. 10, 1935 2,128,178 White Aug. 23, 1938 2,138,224 BaraschNov. 29, 1938 2,200,939 Trebbin May 14, 1940 2,279,831 Lempert Apr. 14,1942

